Sulfonic acid-catalyzed condensation process



United States atent fire 7 3,078,255 SULFONIC AClD-CATALYZEDCONDENSA'HGN PRUQESS Ronaid M. Pike, Chelmsford, Mass., assignor toUnion Carbide Corporation, a corporation of New York No Drawing. FiledDec. 8, 1959, Ser. No. 858,046 11 Claims. (Cl. Mil-46.5)

wherein R is a substituted or unsubstituted monovalent I hydrocarbongroup, R is an alkyl group or a hydrogen atom and n has a value of atleast one can be condensed in the presence of a catalyst (e.g. sulfuricacid or potassium silonolate) to produce a variety of useful diorganosiloxane products.

By way of illustration, it is known that those hydroxylcontainingorganosilicon compounds represented by Formula 1 wherein R and R havethe above-defined meanings and n has a value from 1 to 7 can becondensed to form cyclic diorganosiloxanes (i.e. diorganosiloxanetrimers to heptamers) which can be separated from the reaction mixturefree of most of the monofunctionad and trifunctional impurities thatoften contaminate the hydroxyl-containing organosilicon compounds. Thesepure cyclic diorganosiloxanes can then be used in conventionalapplications wherein monofunctional and trifunctional impurities producedeleterious eifects (e.g. in the production of gums for use in producingsilicone elastomers). However, the catalysts currently employed ineffecting the condensation of hydroxyl-Containing organosiliconcompounds also-catalyze the equilibration of diorganosiloxanes.reactions, the reaction mixture contains 648% by weight of the desiredlow molecular weight cyclic diorganosiloxanes and 82-94% by weight ofhigher molecular weight linear diorganopolysiloxane oils or gums. Theequilibrium concentration of such low molecular weight cyclicdiorganosiloxanes is conventionally increased above 18% by conductingthe condensation in a solvent but, upon removal of the solvent from suchreaction mixtures, the

equilibrium concentration of these cyclic diorganosilox-' anes revertsto 618% byweight unless the catalyst is also removed. Alternately,yields of the desired cyclic disiloxanes are thereby caused todepolymerize continuously to maintain the equilibrium concentration ofthe desired cyclic diorganosiloxanes in the reaction mixture. Thenecessity for such distillation operations increases process costs andso constitutes an undesirable feature of such processes.

As a further illustration, it is known that those hydroxylcontainingorganosilicon compounds represented'by Formula 1 wherein R and R havethe above-defined meanings and n has a value of at least 8 can becondensed to form diorganopolysiloxane oils and gums that can beemployed, for example, in producing silicone elastomers. However,aspointed out above, the catalysts currently employed in effecting thecondensation of hydroxyl-containing organosilicon compounds alsocatalyze equilibration reactions andso 6-18% by weight of the desireddiorganopolysiloxane oils and gums are converted to lower molecularweight When equilibrium is reached in such equilibrium 2 cyclicdiorganosiloxan'es- (i.e. mostly diorganosiloxane cyclic trimers andtetramers) the desired diorgan'opolysiloxaneoils and gums are 'diminished and the oilsand gums are contaminated by'6- 18% by weight of thelow molecular weight cyclic diorgano= siloxanes.

This invention is based on the'discovery'that certain? organic sulfonicacids catalyze'thecondensation of hydroxyl-containing' organosiliconcompounds represented by Formula 1 but do not catalyze the equilibrationof diorganosiloxanes to a significant extent.

containing org'anosilicon compoundsin the presence of'a catalytic amountof anar'yl' sulfonic' acid or a sulfoalka noic acid.

The condensation catalysts employed in this invention are organicsulfonic acids and, in particular, aryl sulfonic' Illustrative of thearyl sul-' fonic acids employed as catalysts in this invention'are'phenyl sulfonic acid, o-toluene sulfonic acid, m-toluene' acids andsulfoalkanoic acids.

sulfonic'acid, p-toluene' sulfonic acid and alpha naphthylene sulfonicacid. Illustrative of the sulfoalkanoic acids" employed ascatalysts inthisinvention are gamma-sulfobutyric acid, gamma-sulfopentanoic acid,delta-sulfohefi anoic acid, alpha-sulfopalmitic acid andalpha-sulfostearic' acid. The preferred catalysts are p-toluene sulfonic acid,alpha-sulfopalmi'ticacid and 'alpha sulfos'tearic acid. The catalystscan be employed as such or in the form of" their hydrates whichdecompose to produce the catalyst during the condensation reaction.

The hydroxyl-containing organosilicon compounds emplayed in thisinvention'are represented by'Formula'lp Illustrative ofthe'unsubstituted monovalenthydrocarbori groups represented by R inFormula 1 are the alkyl groups-f (e.g. the methyl, ethyl and octadecylgroups), the cycloalkyl groups (e.g. the cyclohexyl and the cyclopentylgroups), the aryl groups (e.g. the phenyl, tolyl, xylyl and naphthylgroups), the'aralkyl groups (e.g. the benzyland beta-phenylethylgroups), the alkenyl groups (e.g. the

vinyl, allyl and hexenyl groups) and the cycloalkenyl' v Illustrative ofthe substituted monovalent hydrocarbon groups represented by R inFormula 1 are the alkyl, cycloalkyl, aryl, ,aralkyl, alkenyl andcycloalkenyl groups containing as substituents one or more halogen atomsor cyano, hydroxyl or hydro- Thesesubstituents do not reactto anysignificant extent during thegroups (e.g. the cyclohexenyl groups).

carbonoxy (e.g. alkoxy or aryloxy) groups.

condensation reaction. The groups represented by R in Formula 1preferably contain from 1 to 10 carbon atoms. Illustrative of the alkylgroups represented by R in? Formula 1 are the methyl, ethyl and propylgroups. In Formula I n can represent an average value in those caseswhere mixtures of hydroxyl-containing organosilicon com pounds areemployed.

Typical of the hydroxyl-containing organosilicon'com pounds representedby Formula 1 are those :that are'more Me R (5) Patented Feb.- 19, 1963Consequently, the yield 'of This invention provides a process whichinvolves condensing hydroxylamazes wherein n, p and q each have a valueof at least one, and R is a methyl or an ethyl group. As used herein Medenotes the methyl group and Vi denotes the vinyl group.

The hydroxyl-containing organosilicon compounds employed in thisinvention can be produced by known proc esses. By one such knownprocess, a diorganodialkoxysilane is completely hydrolyzed and partiallycondensed in amixture of a water and a solvent (e.g. ether), to producea suitable hydroXy-containing reactant; or a diorganodialkoxysilane ispartially hydrolyzed and partially condensed to produce a suitablealkoxyand hydroxy-containing reactant. By another such known process, acyclic diorganosiloxane is reacted with steam at an elevated temperatureand pressure to produce a suitable hydroxy-com taining reactant.

In general from 0.001 part to 20 parts by weight of the condensationcatalyst per 100 parts by weight of the starting hydroXyl-containingorganosilicon compounds are useful in the process of this invention.From 0.1 part to 10 parts of the catalyst per 100 parts by weight of thestarting organosilicon compound are preferred. Although other than theindicated amounts of catalyst can be used, no commensurate advantage isgained thereby.

The process of this invention is advantageously conducted at atemperature from 25 C. to 170 C. However, the process is preferablyconducted at a temperature from 120 C. to 150 C. Adherence to theindicated temperature ranges is generally desirable but not critical.

The process of this invention involves a condensation reaction thatproduces water as a by product and that can be represented by theskeletal equation:

-:SiH+H0s:it%1os i +H0 When hydroxyl-containing organosilicon compoundsrepresented by Formula 1 wherein R is an alkyl group are employed,condensation reactions represented by the following skeletal equationcan also occur to produce an alcohol as a by product:

However, in the latter case, the reaction represented by Equation 6occurs concurrently and at a faster rate. The water or the water andalcohol produced as a by product is preferably continuously removed fromthe reaction mixture during the reaction by suitable means, e.g. byheating the reaction mixture at reduced pressure (preferably from 1 to10 mm. of Hg) to the above-mentioned preferred temperatures tovolatilize the water or water and alcohol.

The hydroxyl-containing organosilicon compounds and the catalyst can bedissolved in an inert liquid organic compound in which they are mutuallysoluble and the process of this invention can be conducted therein.Suitable liquid organic compounds are ethers (e.g. diethyl ether andn-butyl ether), aromatic hydrocarbons (e.g. xylene and toluene) andaliphatic hydrocarbons (e.g. ndecane). Amounts of these liquid organiccompounds from 10 parts to 1000 parts by weight per 100 parts by weightof the starting hydroxyl-containing organosilicon compounds are usefulbut amounts of the liquid organic compounds from 50 parts to 200 partsby Weight per 100 parts by weight of the starting hydroxyl-containingorganosilicon compounds are preferred. At the completion of the process,the liquid organic compound can be removed from the desireddiorganosiloxane by any suitable means, e.g. by heating the reactionmixture to a temperature sufiiciently elevated to volatilize the liquidorganic compound.

At the completion of the process of this invention the catalyst can beremoved from the desired diorganosiloxane by any suitable means. By wayof illustration, the sulfonic acid can be removed from thediorganopolysiloxane by washing the diorganopolysiloxane with water.

Those hydroxyl-co'ntaining organosilicon compounds 4- that arerepresented by Formula 1 wherein R and R have the above-defined meaningsand n has a value from 1 to 7 are condensed according to the process ofthis invention to produce mixtures containing cyclic diorganosiloxaneshaving the formula:

(R SiO) (8) wherein R has the above-defined meaning and p has a valuefrom 3 to 7 and higher molecular Weight linear diorganopolysiloxanes.When the condensation of the latter-mentioned hydroXyl-containingorganosilicon compounds is conducted in the above-mentioned solvents,yields of cyclic diorganosiloxanes represented by Formula 8 as high as40% are obtained. Owing to the fact that the catalysts employed in thisinvention do not catalyze the equilibration of cyclic diorganosiloxanesrepresented by Formula 8 to form higher molecular weightdiorganopolysiloxanes, the yield of these cyclic diorganosiloxanes isnot reduced by such reactions when the solvent is removed. Continuousdistillation of such cyclic diorganosiloxanes from the reaction mixtureis not necessary to obtain yields as high as 40%.

Those hydroxyl-containing organosilicon compounds that are representedby Formula 1 wherein R and R have the above-defined meanings and n has avalue of at least eight are condensed according to the process of thisinvention to produce linear diorganosiloxanes having the formula:

wherein R and R have the above-defined meaning and q has an averagevalue of at least 16. Owing to the fact that the catalysts employed inthis invention do not catalyze the equilibration of suchdimethylpolysiloxanes, these dimethylpolysiloxanes are producedessentially free of low molecular weight cyclic siloxanes (i.e. theycontain from 0% to 3% by weight of such cyclic siloxanes).

In the production of linear diorganopolysiloxanes represented by Formula9 according to the process of this invention, the initial product is anoil. As the process is continued the viscosity of the oil increasesuntil, in the case of alkoxy containing hydroxyl-containingorganosilicon compounds, a stable alkoxy end-blockeddiorganopolysiloxane oil is produced. In the latter case, the processcan be stopped at an intermediate point (e.g. by removing the catalyst)to obtain a diorganopolysiloxane oil containing both hydroxyl and alkoxyend-blocking groups. In the case of hydroxyl-containing organosiliconcompounds free of alkoxy groups, the final product is a gum but theprocess can be stopped at an intermediate point to produce a hydroxylend-blocked diorganopolysiloxane oil.

The diorganopolysiloxane oils produced in accordance with the process ofthis invention are preferably those represented by Formula 9 wherein Rand R have the above-defined means and q has a value from 200 to 4000.These oils can be produced by conducting the process until the viscosityor any other conveniently measured property of the oil indicates thatthe desired molecular weight has been obtained and then removing thecatalyst by any suitable means (e.g. by Washing the oil with water todissolve the catalyst).

The diorganopolysiloxane gums produced in accordance with the process ofthis invention are preferably those represented by Formula 9 wherein Rand R have the above-defined meanings and q has a value from 6000 to15000. The gums can be produced by conducting the process until thehardness (as measured, for example, by a Miniature Penetrometer) or anyother conveniently measured property indicates that the desiredmolecular weight has been obtained and then removing the catalyst by anysuitable means (e.g. by washing the gum with water).

F 6 Those diorganopolysiloxane,oils produced in accordance withtheprocess of this invention that contain hydroxyl end-blocking groupsundergo a gradual increase in viscosity owing to the condensation ofthese hydroxyl groups, especially if the oilsare exposed to elevatedtemperatures. These oils can be stabilized against such increases inviscosity by reacting the oils with trihydrocarbonhalosilanes (e.g.trimethylchlorosilane) in order to convert the hydroxyl groups to stabletrihydrocarbonsiloxy groups as illustrated by the equation:

wherein R and R have the above-defined meanings and r has a value from 1to 3. Such cocondensations involve reactions that can be represented byEquation 7. These cocondensations are useful in producingdiorganosiloxanes containing functional groups uniformly spacedthroughout the siloxane chain or at the end of the siloxane chain. Byway of illustration, a hydroxyl-containing dimethylpolysiloxane can becocondensed with methylvinyldiethoxysilane to produce a siloxanecontaining uniformly spaced vinyl groups according to the equation:

I no (MeQSiOMQH MeSi(O can).

Vi Vi I I 02115011 H (MegSiOh SiO (MczSiO) 20 (Mez iOMH Me Me wherein xis an integer. The siloxane so produced can be cured through the vinylgroups to produce a silicone gum. As a further illustration,hydroxyl-containing dimethylpolysiloxanes [e.g.-HO(Me SiO) H] can becocondensed with methyltriethoxysilane to produce a siloxane containinguniformly spaced ethoxy groups which canbe hydrolyzed and condensed toconvert the siloxane to a silicone resin. As another illustration, ahydroxyl-containing dimethylpolysiloxane [c.g. HO(Me SiO) H] can be.cocondensed with gammahydroxypropyldimethylethoxysilane to produce asiloxane containing gamma-hydroxylpropyl chain terminating groups.

Illustrative of the alkoxysilanes represented by Formula 11 are:methyltriethoxysilane, methylvinyldiethoxysilane,gamma-cyanopropylmethyldiethoxysilane, dimethyldiethoxysilane,trimethylethoxysilane and gamma-hydroxypropyldimethylethoxysilane.

The diorganosiloxanes that are produced in accordance with the processof this invention are known compounds that are useful in a variety ofapplications. Thus the cyclic diorganosiloxanes can be converted to gumswhich can be used in producing silicone elastomers, thediorganopolysiloxane oils can be used as hydraulic fluids and thediorganopolysiloxane gums can be used in producing silicone elastomers.

The following examples illustrate the present invention.

Example I A mixture was formed containing 265 grams of HO(Me SiO) I-Iand grams of HO(Me SiO) (MeViSiO)H The mixture was heated at 90 C. at2.0 mm. of Hg for 0.5 hours to remove any volatile materials.Para-toluene sulfonic acid monohydrate (0.04 gram) was added to themixture and the heating at C.Lat 2.0 mm; of Hg was continued for twohours during which time the viscosity of the mixture increased. Another0.4 gram of the mono-. hydrate was added and the heating was continuedfor- 2.5 hours. Then the temperature was raised to 150 C. and themixture was heated for two hours at 2.0 mm. of Hg to produce a gum thatwas soluble in chloroform and toluene.

The gum so produced grams), a silica filler (40 grams) and a peroxidecuring agent (1.5 grams) were mixedand cured and then postcured toproduce an elas-- tomer. Theliuear shrinkage of the elastomer duringpostcure was 3.4% dueto curing and thermal shrinkage For comparisonpurposes, a similarsilicone elastomer produced from a gum that had-beenof the elastomer.

prepared by known procedures was found to undergo a 6.2% linearshrinkage when similarly postcured due to curing and thermal shrinkageof the elastomer and volatilization of low molecular weightdimethylsiloxanes.

The difference in shrinkage of the elastomers during postcure was due tothe substantial absence of low molecularweight dimethylsiloxanes in theformer gum (i.e.-

the gum produced by the process of this invention).

Example I] Equivalent results to those obtained in Example I areobtained when alpha-sulfostearicacid or alpha-sulfopalmitic acid is usedin lieu of para-toluene sulfonic acid. as the condensation catalyst.

What is claimed is: I

1.A process for condensing organosilicon compounds represented by theformula:

f H0(s i0)..R'

wherein .R is a memberselected from the group consisting of. theunsubstituted monovalent hydrocarbon groups and; the substitutedmonovalent hydrocarbon groups wherein.

each substituent is a memberselected from the group of the halogen atom,and the cyano, hydroxyl, alkoxyl and aryloxy groups, R is a memberselected from the group consisting of. the. alkyl groups and thehydrogen atom and'n has a value of at least one, which process comprisescondensing an organosilicon compound represented by said formula in thepresence of a catalytic amount ofa member selected from the groupconsisting of the aryl sulfonic acids and the sulfoalkanoic acids eachof said acids containing no more than. 18 carbon atoms.

2. A process for condensing organosilicon compounds represented by theformula: i H0(S i0)nR' wherein R is an alkyl group and n has a valuefrom 1 to 7 and R is a member selected from the group consisting of thealkyl groups and the hydrogen atom to produce cyclic diorganosiloxanesrepresented by the formula:

(R2810 3 wherein R has the above-defined meaning and p has a value from3 to 7, which process comprises condensing an organosilicon compoundrepresented by Formula A in the presence of a catalytic amount of anaryl sulfonic acid that contains no more than 18 carbon atoms to producea cyclic diorganosiloxane represented by Formula B.

3. A process for condensing organosilicon compounds represented by theformula:

R Ho(dio)..R'

7 wherein R is an allryl group, n has a value of at least eight and R'is a member selected from the group consisting of the alkyl group andthe hydrogen atom to produce linear diorganopolysiloxanes having theformula:

R (B) wherein R and R have the above-defined meanings and q has anaverage value of at least sixteen, which process comprises condensing anorganosilicon compound represented by Formula A in the presence of acatalytic amount of a sulfoalkanoic acid that contains no more than 18carbon atoms to produce a linear diorganopolysiloxane composed of groupsrepresented by Formula B.

4. A process for condensing organosilicon compounds represented by theformula:

ltlle HO (SiO) 1111 wherein n has a value of at least eight to produce adiorganopolysiloxane gum, which process comprises heating anorganosilicon compound represented by said formula to a temperature from25 C. to 170 C. in the presence of from 0.001 part to 20 parts per 100parts of the organosilicon compound of a toluene sulfonic acid toproduce a gum.

5. A process for condensing an organosilicon compound represented by theformula:

wherein R" is a methyl group, p and q each have a value of at least oneand the sum of p and q has a value of at least eight to produce adiorganopolysiloxane gum, which process comprises heating anorganosilicon compound represented by said formula to a temperature from25 C. to 170 C. in the presence of from 0.001 part to 20 parts per 100parts of the organosiiicon compound of an alpha-sulfoalkanoic acid thatcontains no more than 18 carbon atoms to produce a gum.

6. A process for condensing HO(Me SiO) H wherein n has an average valueof} at least eight, which comprises heating HO(Me SiO) H at atemperature from 120 C. to 150 C. and at reduced pressure in thepresence of from 0.1 to parts of p-toluene sulfonic acid per 100 partsby weight of the HO(Me SiO) H to produce a dirnethylpolysiloxane gum.

7. A process for condensing HO(Me SiO) H wherein n has an average valueof at least eight, which comprises heating HO(Me SiO) I-I at atemperature from 120 C. to 150 C. and at reduced pressure in thepresence of from 0.1 to 10 parts of alpha-sulfostearic acid per parts byweight of the HO(Me SiO) I-I to produce a dimethylpolysiloxane gum.

8. A process for condensing HO(Me SiO) H wherein n has an average value013 at least eight, which comprises heating HO(Me SiO) H at atemperature from C. to C. and at reduced pressure in the presence offrom 0.1 to 10 parts of alpha-sulfopalmitic acid per 100 parts by weightof the HO(Me SiO) I-I to produce a dimethylpolysiloxane gum.

9. A process which comprises cocondensing (1) an organosilicon compoundrepresented by the formula:

wherein R is a member selected from the group consisting theunsubtituted monovalent hydrocarbon groups and the substitutedmonovalent hydrocarbon groups wherein each substituent is a memberselected from the group consisting of the halogen atoms and thehydroxyl, cyano, alkoxy and aryloxy groups, R is a member selected fromthe group consisting of the alkyl groups and the hydrogen atom and n hasa value of at least eight and (2) and allcoxysilane represented by theformula:

I K lb-r wherein R and R have the above-defined meanings and r has avalue from 1 to 3, said cocondensation being etfected in the presence ofa catalytic amount of a member selected from the group consisting of thearyl sulfonic acids and the sulfoalkanoic acids each of said acidscontaining no more than 18 carbon atoms.

10. The process of claim 9 wherein the alkoxysilane ismethyltriethoxysilane.

11. The process of claim 9 wherein the alkoxysilane ismethylvinyldiethoxysilane.

References Cited in the file of this patent UNITED STATES PATENTS2,371,068 Rochow Mar. 6, 1945 2,843,555 Berridge July 15, 1958 2,916,507erschner et a1 Dec. 8, 1959 FOREIGN PATENTS 570,580 Canada Feb. 10, 1959

1. A PROCESS FOR CONDENSING ORGANOSILICON COMPOUNDS REPRESENTED BY THEFORMULA: